1. Field of the Invention
The invention relates in general to a system and method of substrate handling in semiconductor processing, and specifically to a robot arm with primary and secondary substrate locations on a paddle-type end effector.
2. Description of the Related Art
In the processing of semiconductor devices, such as transistors, diodes, and integrated circuits, a plurality of such devices are fabricated simultaneously on a thin slice of semiconductor material, termed a substrate or wafer. Such wafers are extremely brittle, and easily contaminated. During manufacturing of semiconductor integrated circuits, therefore, care must be taken to avoid physical damage and particulate contamination to the wafers.
Various systems are known for handling wafers within semiconductor processing systems. The particular application or environment from which the wafer is lifted often determines the type of pickup device. One class of pickup devices, known as Bernoulli wands are typically used for high temperature applications. Bernoulli wands utilize jets of gas downward from the wand toward the wafer to create a region of low pressure above the wafer, therefore lifting it. The advantage being that the hot wafer need not contact the pickup wand, except perhaps at one or more small locators depending from the wand. Such a Bernoulli wand is shown in U.S. Pat. No. 5,080,549 to Goodwin, et al.
Another type of wafer pickup device is a simple paddle which relies on friction due to gravity between wafer support surfaces and the back of the wafer. In a variation of that, the paddle is augmented with a vacuum to hold the wafers on the paddles.
U.S. Pat. No. 5,135,349 to Lorenz, et al., discloses a robotic handling system utilizing two paddle style pickups mounted on a common rotating base. Both pickups are adapted to extend linearly away from one another to speed up handling of wafers within the processing system. Again, the paddles are augmented with a vacuum generated through a plurality of holes in an end effector portion of each paddle.
In a more recent method of wafer handling, a dual-arm transfer assembly is provided with one arm having a spatula-type end effector, and the other a Bernoulli wand end effector. This method uses the spatula to retrieve or deposit a wafer from or to a cassette. Prior to insertion into the process chamber for deposition, the wafer is xe2x80x9chanded offxe2x80x9d to the Bernoulli wand, which then places the wafer into the process chamber. Following processing, the Bernoulli wand retrieves the wafer from the process chamber and retracts it into the wafer handling chamber, where the wafer is deposited in a cooling station. When sufficiently cool, the spatula is used to return the wafer to the cassette in the load lock. This sequence of placing/retrieving a wafer from the cool station and returning it to it""s cassette, fetching the next wafer and returning to the Bernoulli hand-off position is relatively short, but yet reducing the time is desirable. These robotic motions are typically conducted during the etch cycle where the process chamber is not available to process wafers. As improvements are made in process technology, the etch cycle may be significantly shortened or eliminated. Hence, there is a need for a system that reduces wafer handling time.
It is therefore one object of the present invention to provide a first robot arm with a paddle-type end effector capable of holding two substrates at primary and secondary locations. This arm is preferably to be used in conjunction with a second robot arm having a Bernoulli wand end effector, both of which are actors in a pivoting linear robot. The secondary location is effectively a staging area for a wafer prior to its being processed. By using the Bernoulli wand to retrieve a hot, processed wafer, placing that wafer on the cooling station, and having another wafer staged on the secondary location on the paddle, the loading time of the next wafer into the process chamber may be significantly reduced. This effectively results in a significant improvement in throughput for the overall wafer processing system.
The two robot arms are mounted such that they can translate linearly within a wafer handler of the semiconductor processing system. A wafer can be moved in and out of a cassette of many wafers staged in a load lock chamber. The cassette or the paddle may be independently vertically movable such that the paddle can be positioned underneath a wafer and lift it from the cassette.
In order to transfer a wafer from the primary location to the secondary location, the first robot arm returns to its xe2x80x9chomexe2x80x9d position which places the wafer on the primary location directly below the Bernoulli wand. The Bernoulli wand then lifts the wafer from the paddle by initiating the flow of gas through the Bernoulli wand, creating a low pressure region above the wafer, and thus lifting it. Once the wafer has been lifted by the Bernoulli wand, the first robot arm translates forward to a position such that the secondary wafer location is directly below the wafer being held by the Bernoulli wand. The wafer is then deposited onto the paddle at the secondary position by stopping the flow of gas through the Bernoulli wand. The paddle is then retracted to the xe2x80x9chomexe2x80x9d position. Note that this is done while a wafer, previously deposited in the process chamber, is processing so as not add to the overall cycle time.
The Bernoulli wand then translates forward and into the process chamber in order to retrieve a xe2x80x9chotxe2x80x9d processed wafer. The xe2x80x9chotxe2x80x9d wafer is lifted by the Bernoulli wand as described above, and the wand is then retracted to its xe2x80x9chomexe2x80x9d position. Assuming the paddle is made of material which can handle the heat, such as quartz, the hot wafer is dropped on the paddle at the primary position. Next, the paddle extends toward the process chamber to the point which the xe2x80x9ccoldxe2x80x9d wafer in position two is under the wand. Then the wand lifts the xe2x80x9ccoldxe2x80x9d wafer and the paddle retracts to its home position. The wand then places the xe2x80x9ccoldxe2x80x9d wafer in the reactor and retracts to its xe2x80x9chomexe2x80x9d position.
The wafer handler then rotates to face the cooling station where the xe2x80x9chot wafer is deposited for cooling. The handler can then be rotated to retrieve another xe2x80x9ccoldxe2x80x9d wafer from the load lock for transfer to the second position on the paddle. The first robot arm can be used to transfer cooled wafers to the load lock while waiting for a wafer to be processed.
In an alternate sequence, a xe2x80x9chotxe2x80x9d wafer can be deposited directly in a cooling station, and then an unprocessed wafer transferred to the reactor. That leaves the reactor empty longer than in the first described systems, but the paddle is not subjected to the hot wafer. Wafers can be transferred from a cooling station to the load lock while a wafer is in the reactor.